1. Field of the Invention
The present invention relates to a structure of hemmed together metal plate materials, for use of hemming of, for example, outer plates for automobiles such as engine hoods and door panels.
2. Description of Related Art
A hem structure of an outer plate for automobiles is usually formed by folding an edge of an outer panel over edge of an inner panel with a sealant or adhesive applied therebetween for the purpose of bonding. When a thermosetting resin is used as the adhesive, it is heated and cured in an oven or the like after the hemming process.
Thus, since the hemmed together pamels are transported to an oven or the like for curing after the hemming process, the hemmed together panels are not always retained as they are during transport. Accordingly, in order to retain the hemmed together pamels until the adhesive completely cures, it has been a conventional manner, for example, to dimple caulking or coining for the purpose of preventing relative movements between the panels (U.S. Pat. No. 5,237,734). As shown in FIGS. 11Axcx9c11C, in dimple caulking 20, a dimple 26 is formed on an inner panel 14 in advance (see FIG. 11B), then an outer panel 12 is turned and pressed to finish hemming (FIG. 11C), whereupon a hem flange 16 is subjected to plastic deformation along the dimple 26 as shown by reference numeral 28 (FIG. 11A).
However, interlocking the hemmed together panels by spot welding has a problem of thermal distortion as a result of welding heat. Particularly, the outer side of the outer panel is the surface of the product and is required to be carefully finished to have a good appearance. Accordingly, it becomes necessary to eliminate such distortion by surface finishing.
Also, in the method of dimple caulking, it is very difficult to make center alignment between the escape portion of a hemming die and the inner panel. That is, it is very difficult to make the hemming die pressing direction match the dimple shape of the press die, and after all, the job has to be done at the site. It is clear that generation of disalignment causes marks to remain on the outer surface of the outer panel. Furthermore, in the hemming process, there is no problem because of forming a dimple on the inner panel in advance, but the outer panel itself has a shape (for example, in the case of a door panel, it has a substantial curvature at the top close to the roof), there exists a problem that a dimple cannot be properly formed by a press that makes a vertical motion. Consequently, adaptable portions will be very much limited.
Furthermore, in order to more securely retain the panels, a dimple portion is sometimes welded as by a laser beam. In this case, however, the laser beam is applied to the spherical surface of the dimple and it is very difficult to control the height of the dimple and also to release the gas decomposed from the adhesive due to heat generated during laser welding or to control dimple clearance.
An object of the present invention is to provide a structure capable of reliably retaining the hemmed together panels without requiring any complicated operations.
The present invention provides a structure of hemmed together metal plate materials with an edge portion of an outer panel hemmed over an edge portion of an inner panel, characterized in that the edge portion of the inner panel has an inside rise portion having a surface plane down-sloping towards an edge thereof and the edge portion of the outer panel has an outside rise portion telescopically fitted with the inside rise portion, a back plane of the outside rise portion abutting on the surface plane of the inside rise portion. Here, the metal includes aluminum and other non-ferrous metals or alloy besides iron and steel.
In accordance with the present invention, the inside rise portion formed at the edge portion of the inner panel in advance is telescopically fitted with the outside rise portion formed during complete hem forming of the outer panel, thereby assuring reliable retention without deflection between the inner panel and the outer panel. Accordingly, even in the case of applying adhesive, both panels will be securely retained until the adhesive cures. Particularly, since a sturdy structure is formed in a way of caulking with the inside and outside rise portions fitted with each other, it is possible to completely prevent relative movement between the panels at least in a direction parallel to the edge of the inner panel.
As for the present invention, it can be said that the shape of a dimple in dimple caulking has been changed from a spherical surface to a plane surface. In a conventional method of dimple caulking, a spherical dimple is formed by pressing an inner panel, and an outer panel is similarly pressed and formed along the spherical profile, which will not assure a tight fitting finish. On the other hand, in the present invention, since the surface plane at top of the inside rise portion abuts on the back plane at top of the outside rise portion, the pressing direction and the caulking position can be freely determined, and moreover, it is possible to very easily perform laser welding or the like for complete retention after the caulking (hemming) process and to visually control and actually measure the clearance for escape of the gas decomposed from the adhesive that often causes a problem in quality assurance and execution of welding. Also, it becomes easier to adjust the strength of push against the hem by clamping both sides of the rise portion.
According to an embodiment of the present invention, the plane shape of the rise portions is rectangular. Two sides of a rise portion in a direction crossing the edge of an inner panel may be either parallel or non-parallel to each other (see FIG. 5). As an example of a non-parallel fashion, when the sides diverge as they approach the edge of the inner panel (FIG. 5B), which is advantageous in that the inner panel is prevented from displacing in the direction of removal in which it comes out of the hem flange of the outer panel.
According to an embodiment of the present invention, the inside rise portion is welded to the outside rise portion (FIG. 9). Since these rise portions are in plane-to-plane abutting relation with each other, it is easy to weld them tight to each other, for example, by laser welding. Also, because of a space existing between the inside rise portion and the outer panel, there is no fear of affecting the surface of the outer panel due to heat generated during the welding operation.